While most land vehicles, such as automobiles, trucks, etc. and many light aircraft are powered by internal combustion engines, a number of other drive systems have been proposed. These include gas turbine engines, steam engines, electric battery power, etc. and combinations of these systems. Because of the high state of development of the internal combustion engine and the low efficiency, short range and other problems, none of these alternative systems have come into widespread use.
Today, with increasing environmental awareness and increasing efforts to reduce pollution, greater attention is being given to drive systems which produce less air pollution than internal combustion engines. Also, internal combustion engines are not fully efficient, wasting considerable amounts of energy in the form of heat that must be passed to the atmosphere though a radiator and exhaust system.
A number of different compressed air powered vehicles have been developed, either fully powered by compressed air or as an assist system to supplement an internal combustion engine. Compressed air drive is quiet, generally has few objectionable emissions and can recover energy wasted during braking and emit little waste heat energy.
Typical air assist or hybrid systems are described by Ellison in U.S. Pat. No. 4,123,910. An air compressor is powered by a main, internal combustion, engine. The internal combustion engine is used when speeds are in the range in which that engine is most efficient. During driving under conditions in which the main engine is inefficient, such as stop-and-go urban driving, the compressed air powers the same drive train with the main engine turned off. While improving efficiency under limited conditions, this system still has most of the disadvantages of the internal combustion engine and is very heavy, requiring both internal combustion and air drive system, reducing efficiency.
Another hybrid system, requiring an electric motor and flywheel drive for an air compressor is described by Yeh in U.S. Pat. No. 4,163,367, and has similar problems with weight and complexity. Other hybrid combinations of an internal combustion engine or battery for compressing air are described by Gardner in U.S. Pat. Nos. 4,590,767 and 4,753,078 and have the same weight and efficiency problems.
An auxiliary system for using braking energy to compress air to supplement a main engine is described by Lowther in U.S. Pat. No. 4,290,268. A similar system is described by Chang in U.S. Pat. No. 4,798,053. Again, as merely a supplement to a main engine, the weight, complexity and cost of the auxiliary system is not generally justified by any efficiency increases.
In U.S. Pat. No. 4,383,589 Fox describes a system using a drive system for each wheel consisting of a motor powered by compressed air from a tank. A compressor is connected to each wheel to feed compressed air to the tank. Since no source of energy is furnished to replenish energy lost to friction in the system, the tank will quickly run out of air. Even if the tank were filled before beginning a drive, the vehicle would have an extremely short range.
Thus, there is a continuing need for improved vehicle drive systems that are more energy efficient, produce less pollution, transfer power to the motive means in a less complex, lighter weight and more effective manner and recover and use energy dissipated during breaking and coasting.